A question was posed to me this morning. How can I change the character width (not the Mtext box width) on hundreds of Mtext objects? The quickest way I could come up with, without having to write a lisp routine is this.
Create a new textstyle with the desired width factor. Set all of the other properties to the same as your existing Mtext objects (Font, Oblique Angle, etc). Now select the multiple Mtext objects (use Qselect if needed) and then set the Style to your new textstyle. This should overwrite the properties of the characters in the mtext block to take on the properties of the new textstyle. In some cases, you may need to strip out hardcoded internal properties from the Mtext characters. See this post for more details: How to remove unwanted formatting from AutoCAD Text with StripMtext Lisp
Obviously if your existing mtext objects vary in font, this won’t work unless you repeat for each font used.